Thermoset resins are materials that cure to form very hard plastics. These materials that can be used in a wide variety of consumer and industrial products. For example, thermosets are used in protective coatings, adhesives, electronic laminates (such as those used in the fabrication of computer circuit boards), flooring and paving applications, glass fiber-reinforced pipes, and automotive parts (including leaf springs, pumps, and electrical components). Relative to other types of plastics, cured thermosets are typically brittle. It would therefore be desirable to retain the good properties of thermosets and also reduce their brittleness.
Poly(arylene ether) resins, sometimes called polyphenylene ethers, have been disclosed as additives to reduce the brittleness (improve the toughness) of cured thermosets. For example, it is known to combine certain poly(arylene ether) resins with thermosets resins such as epoxies, cyanate esters, maleimides, acrylates, and benzoxazine resins. These poly(arylene ether)-containing compositions are often processed in solvents to reduce the viscosity of the curable composition and to enhance impregnation of the curable composition into fillers and/or reinforcements. When a solvent is used, it would be preferable to use a non-chlorinated hydrocarbon solvent. However, non-chlorinated hydrocarbon solvents such as N-methyl-2-pyrrolidone (NMP) and methyl ethyl ketone (MEK) are not ideal for this purpose because they produce phase-separated mixtures with most poly(2,6-dimethyl-1,4-phenylene ether)s at room temperature. Improvements in the miscibility of poly(arylene ether)s and solvents have been obtained by processing curable compositions containing them at elevated temperatures as described, for example, in Japanese Patent Application Publication No. JP 06-220226 A of Katayose et al. However, it would be desirable to avoid the use of elevated temperatures because they are associated with increased solvent flammability, increased solvent emissions, and increased energy costs. It would also be desirable to have concentrated solutions of poly(arylene ether)s so that higher concentrations of dissolved poly(arylene ether) could be added to a thermoset composition without also adding large amounts of solvent to the composition. Furthermore, in order to facilitate distribution of poly(arylene ether) solutions via truck and rail, it would be desirable to have concentrated solutions of poly(arylene ether)s that can withstand exposure to freezing and sub-freezing temperatures without forming precipitates. There is therefore a need to develop materials and methods for providing solutions in which high concentrations of poly(arylene ether) are soluble at and below room temperature in non-halogenated solvents such as NMP and MEK.